1. RATIONALE

A primary goal of coordinated research on South Florida's environmental resources is to understand those communities as whole ecosystems. Toward that end, the Across Trophic Levels System Simulation (ATLSS) project is an attempt to simulate the interactions of the various elements of wetland biotic communities within the framework of a single, encompassing computational scheme.

The resulting ATLSS model is one of the most complex and sophisticated models ever attempted. It will consist of simulation modules of varying and often very high complexity that represent the important components of the ecosystems of South Florida. It follows that the output from ATLSS will be exceedingly complicated, and it may not be a straightforward task to elucidate the causal origins of any particular model behavior. Such uncertainty could become problematical, especially if the initial trials of ATLSS should behave "pathologically" (as is highly probable during the initial runs of such a complex model). Even should outputs not appear unrealistic, the difficulty remains that there exist no precedents for evaluating how well such a "multi-model" performs as an analog of the real system. I.e., there are no set protocols for "calibrating" such complex simulations. ATLSS, therefore, requires a partially independent benchmark against which one may gauge the plausibility of its outputs; and, towards that end, ATLSS investigators have chosen to create a suite of trophic flow networks that estimate material exchanges in the ecosystems being modeled. These will serve as calibration standards. In addition, these networks will be analyzed by a set of quantitative methods called Network Analysis (NA) that will provide useful information for calibrating the model and important clues for debugging the initial modeling trials.

Trophic flow networks are graphical and mathematical depictions of the answers to the questions, "Who eats whom, and by how much?" Typically, diagrams of flow networks are comprised of boxes that represent the major components of the ecosystem. The boxes are connected by arrows, which indicate the transfers of material or energy between the components. Usually, each arrow is labeled with the magnitude of its transfer as averaged over a prescribed period of time.

Accordingly, the University of Maryland contingent of ATLSS investigators is assembling very detailed networks of carbon exchanges as they normally occur in the ecosystems of South Florida. Networks consisting of more than 60 important compartments are being estimated for each of four habitats, using existing data and ongoing field work. Separate networks for wet and dry seasons are being created for the ecosystems of the forested wetlands, the gramminoid marshes, the mangrove estuaries, and the shallows of Florida Bay. Each network will be a snapshot of the trophic flows and biomasses as averaged both over the hydroperiod in question and over the spatial domain of that particular biotope.

Analyses are to be performed on the resulting networks at several scales. The key questions that can be answered for any fully- quantified trophic network include: (1) To what extent does each taxon depend upon (or contribute to) all other taxa over all trophic pathways, both direct and indirect? (2) What are the efficiencies with which material is being transferred up the trophic ladder? (3) What are the pathways by which material is being recycled within the system? and (4) What is the current organizational status of the ecosystem? Any or all of these answers can be used to debug an ATLSS model that is not performing realistically.

During the 1996 Calendar Year we reported our findings on the cypress wetland ecosystems, as summarized in the introductory material. The 1997 Calendar Year was devoted to elucidating the flows in the ecosystem of Florida Bay (also summarized above), and the elucidation and analysis of the third of these four habitats - the Mangrove Ecosystem- are presented below. In the next annual report (May, 2000) we will present the corresponding results for the networks of the gramminoid wetlands (or Everglades proper).

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